Chris with the 50d you will need a fast card to cope with the cameras 6.3frames /second shooting speed. I use in Brisbane Camera Pro. They state they will price match Australian Prices.
I used on my 50d and also on my new 7d Sandisk Ultras IV or better 4 to 16 gig cards. More expensive for the 45-60mb write speeds but you camera will function to it's full. I had an old cheapy card and the camera would not shoot at it's max speed. Faster cards also better for downloading as well.
Camera Pro are online. Also Photo Continental in Brisbane will try to beat Camera Pro --competition.
Both reliable , not sure if Photo continental do online?? Got my 7d cards and lenses from Camera Pro and extra batteries from Photocontinental.
Just be aware of non Australian supplied items and warrenties.
Mark
P.S. Cheap chips online have good pricing on Cards.